1. Field of the Invention
The present invention relates to a multiple layer composite material comprising at least one layer of cement-bound core concrete and at least one layer of polymer-bound facing concrete, a method for producing the same and to shaped bodies made of said multiple layer composite material.
2. Description of the Prior Art
Concrete is an artificial stone material created by a mixture of cement, concrete aggregate and water, optionally with concrete admixtures and concrete additives, by solidification thereof. Curing is effected by the binding agent cement that sets with the use of water under normal conditions, with a solid body being formed from the pulpy concrete mixture. Possible concrete aggregate, concrete admixtures and concrete additives are mineral as well non-mineral materials of specific sizes (grain gradation). For cement-bound concretes, there have been available, for decades, findings and experience on material features, material composition, material production, material shaping as well as the material behavior both in the fresh and in the cured state. The combined action of cement qualities, aggregates as well as the grain gradation thereof, and of filler materials and other additives as well as the addition of water is known.
Cement-bound concrete is used as building material for example for construction components manufactured in situ or in industrial production, for ready-made concrete parts, such as concrete pipes or concrete ducts, for cladding panels or for paving or plate-like covering elements of concrete, for grass-growing fortification elements or water-permeable pavings.
However, cement-bound concrete has a number of disadvantages: for example, it tends to form efflorescence (of calcium carbonate) or allows water to penetrate the pore structure. For paving or plate-like covering elements of concrete utilized outside, this means that cracks are formed by freezing water in case of frost, which will lead to destruction of the elements in the course of time. Thawing salt used for eliminating ice may enter the plates together with melting water and accelerate their destruction. Due to the porous structure of the surfaces of such coverings, dirt adheres easily thereon, thereby restricting the possibilities of use thereof in areas in which major dirt accumulation is to be expected, such as in goods transshipment areas, industrial filling areas, open-air gastronomy.
For improving the processing properties and properties of use of concrete, materials have been developed in which the usual binder concrete is replaced completely or in part by binder on the basis of synthetic resins, so-called polymer concrete. Suitable binders are, for example, epoxy resin systems, polyurethane resin systems and polyester resin systems.
As compared to conventional cement-bound concrete, polymer-bound concrete has a number of advantages. In particular, it displays higher resistance to chemicals, tends less to dirt adhesion and shows no efflorescence. The mechanical properties of polymer concrete are basically satisfactory as well, such as the slenderness of concrete components made of such concrete, for example polyester concrete channels or polyester concrete pipes.
However, polymer-bound concrete is considerably more expensive to manufacture than cement-bound concrete. Thus, endeavors are made to keep the amount of polymer concrete used as low as possible. However, it is also possible and completely sufficient that a shaped part made of concrete, for example a paving stone or a cladding panel, has only its top side made of polymer concrete.
There are known composite elements in which a prefabricated layer of cement-bound concrete has an also prefabricated layer of polymer-bound concrete adhered thereto. These elements cannot be manufactured in one pass and necessitate expensive special adhesive.
It is also known to form a paving stone as a composite construction of so-called core concrete and facing concrete. The core concrete is cement-bound concrete and the covering layer applied thereto, i.e. the facing concrete, is polymer-bound concrete. These composite elements are manufactured, for example, by first introducing the core concrete mixture, which contains cement as binder, into a mold box of a stone molding machine and then applying the facing concrete mixture, which contains polymer as binder, onto the core concrete mixture. This results in a composite element having a supporting layer of cement-bound core concrete and a usually relative thin covering layer of polymer-bound facing concrete. The properties of the composite element are determined in essence by the covering layer so that only the polymer-bound facing concrete has to fulfill the majority of the requirements to be met by the particular product.
A serious disadvantage of the known paving stones of core concrete and facing concrete consists in that the connection between facing concrete and core concrete is weaker than the bond within the core concrete layer and within the facing concrete layer, respectively. In addition thereto, the known facing concretes have a porous grain structure in which the bond between the aggregate bodies often is created in punctiform fashion only, i.e. there are often materials of quite single-grain gradation adhered to each other at their points of contact. This porous grain structure permits the penetration of water and possibly the penetration of salty solutions during winter. The penetrated water may freeze and cause cracks in the material. In the worst case, the facing concrete layer may chip off from the core concrete layer. The resistance to freeze-thaw cycling of the known paving stones is thus of inferior quality. In addition thereto, the abrasive strength of the porous polymer-bound facing concretes is weak since individual aggregate particles are rapidly torn out of the grain structure if the material is subjected to higher loads, e.g. by being driven on.
It is therefore an object of the present invention to make available a composite material of cement-bound core concrete and polymer-bound facing concrete which overcomes the afore-mentioned disadvantages. In particular, the composite material is to be capable of taking up stresses induced by temperature fluctuations without being damaged and display resistance to freeze-thaw cycling.
Preferably, the composite material also is to be capable of taking up static and dynamic loads, such as xe2x80x9cinstallation stressxe2x80x9d and loads created by being walked on or driven on, without being damaged thereby. Preferably, the composite material also displays resistance to light, in particular UV light, and of course also has the positive properties known with respect to polymer concrete according to the prior art, such as chemical resistance.
Another object of the invention consists in making available shaped bodies of the composite material according to the invention. Such shaped bodies may be e.g. ready-made concrete parts, concrete paving stones or concrete slabs.
An additional object of the present invention consists in making available a method for producing a composite material of cement-bound core concrete and polymer-bound facing concrete. The method is to be suitable to be carried out fully on conventional manufacturing lines for cement-bound concrete, without requiring adaptation measures that are complex in terms of machine technology. Increased demands on the production facilities are to be avoided.
The object is met by the multiple layer composite material comprising at least one layer of a cement-bound concrete, at least one layer of a polymer-bound concrete and a transition between adjacent layers of cement-bound concrete and polymer-bound concrete, wherein the transition has at least the material strength of the less stable one of the adjacent layers, the layer of polymer-bound concrete has a grain structure preventing the passage of liquid water to the transition, but permitting the escape of water, preferably of water in the form of vapor only, from the material, and that the layer of polymer-bound concrete is composed of concrete aggregate, if desired concrete admixtures and/or concrete additives, and of at least one polymer, said at least one polymer or the components of the polymer, in the uncured state, being dispersible in water.
The inventive method for producing the multiple layer composite material, comprising at least one layer of cement-bound concrete, at least one layer of polymer-bound concrete and a transition between adjacent layers of cement-bound concrete and polymer-bound concrete, is characterized by the steps of making at least one concrete mixture containing cement as binder, making at least one concrete mixture containing polymer as binder, with said polymer or the components of said polymer, in the uncured state, being dispersible in water, supplying the concrete mixtures separately and applying them directly on each other so as to form at least one layer of polymer-bound concrete on at least one layer of cement-bound concrete, with the concrete mixture containing cement as binder, at least at the transition between adjacent layers of cement-bound concrete mixture and polymer-bound concrete mixture, containing less water than the amount of water necessary for setting.
A xe2x80x9cpolymer dispersible in water in the uncured statexe2x80x9d is to be understood in the present context to comprise also polymer pre-products or pre-components dispersible in water, for example oligomeric or polymeric compounds that are dispersible in water and are capable of reacting with cross-linkage or additional polymerization and cross-linkage. These polymers or polymer components, after curing, constitute the binder for the polymer-bound concrete.
The shaped body according to the invention that is produced from the multiple layer composite material is provided on at least one surface with at least one layer of polymer-bound concrete.